A conserved non-reproductive GnRH system in chordates

Area of Science:

• Neuroendocrinology
• Chordate evolution
• Comparative physiology

Background:

• Gonadotropin-releasing hormone (GnRH) is crucial for vertebrate reproduction via the hypothalamo-pituitary axis.
• Non-reproductive roles of GnRH are less understood, particularly in early chordates.

Purpose of the Study:

• To investigate the GnRH system in the tunicate Ciona intestinalis.
• To explore the evolutionary origins and functions of GnRH beyond reproduction.

Main Methods:

• Analysis of GnRH and GnRH receptor gene expression in Ciona intestinalis.
• Phylogenetic analysis of tunicate GnRH receptors.
• Functional characterization of GnRH receptor heterodimerization.

Main Results:

• Ciona intestinalis exhibits a widespread GnRH system in its larval nervous system.
• Tunicate GnRH receptors are evolutionarily close to vertebrate receptors but show unique heterodimerization.
• GnRH gene expression in motor ganglion and nerve cord parallels vertebrate hindbrain/spinal cord.
• GnRH receptor expression in tail muscle and notochord suggests non-reproductive roles.

Conclusions:

• Tunicates possess a complex, non-reproductive GnRH system with unique regulatory mechanisms.
• The presence of GnRH in homologous chordate structures suggests an ancient, non-reproductive function.
• This study reveals deep evolutionary origins of non-reproductive GnRH signaling in chordates.